question about gain in microwave amplifier

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ayhz2002

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hi guys:
I designed a single stage amplifier at 5.5 ghZ. I designed the matching networks with smith chart by hand and by using serenade.The matching networks have balanced stubs (open stubs). My design was based on available power gain at 7 dB. Each matching network gives two solutions. When I check the magnitude of S21, sometimes I find it 7.12 dB or 7.29 db or 6.82 db. Can you tell me why?
I don't understand the excess gain I'm geting above 7 dB, why?
I was accurate as much as I can when I designed the matching networks by hand and by serenade. The matching netwroks from serenade and by hand were very close.

any help
thanks
ayhz2002
 

12 paramaters

These gains seem close enough to 7.00. I suspect that the S12 parameter causes the interaction between the input and output matching values.
 

They are actually close and should be acceptable. Remember the mathcing network may also provides some gain because the RF amplefire gain not only depends upon the S21 of device but also on reflected power in the input as well as output.

:!: :idea: :?:

 

It's correct! Infact if you work with the available gain you are introducing an input mismatch, and so due to variation of the input network your input mismatch can change. As a consequence the gain can change.

Bye!
 

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